This invention relates to a method for preparing an optically active succinic acid compound such as .alpha.- or .beta.-methyl succinic acid and derivatives thereof, which is a reaction intermediate useful for synthesis of a variety of physiologically active materials, such as natural products or pharmaceuticals having an optically active carbon, or functional materials, such as low molecular and high molecular liquid crystal materials.
Natural organic compounds having asymmetric carbon usually exist as an optically active material and exhibit physiological activity markedly different from that of enantiomers. For this reason, investigations into catalytic asymmetric synthesis of natural compounds having asymmetric carbon or artificial compounds having asymmetric carbon are proceeding briskly.
Optically active .alpha.-methyl succinic acid can be employed for a variety of fields of application and hence has been prepared by a number of methods. These may be enumerated by a method of optically resolving a racemate produced by reduction of itaconic acid, citraconic acid or mesaconic acid, using quinine or strychnine, as disclosed in, for example, E. Berner and R. Leonardsen, Ann., 538,1 (1939), and a method of asymmetric hydrogenation of itaconic acid using an asymmetric rhodium complex, as disclosed for example in C. Fisher and H. S. Mosher, Tetrahedron Lett., 2487 (1977) and K. Yamamoto, A. Tomita and J. Tsuji, Chem. Lett.,3 (1977).
However, the optical purity of methyl succinic acid produced by these methods is low and amounts only to 52% ee (enantiomer excess) such that the compound can hardly be employed as a starting material for physiologically active materials or functional materials. Although subsequent studies by I. Ojima et al. succeeded in raising the optical purity to the order of 94% ee (I. Ojima, T. Kogure and Y. Yoda, J. Org. Chem., 45,4728 (1980)), the conversion amounts to 94% at most, despite the high hydrogen pressure of 20 atm employed, such that the non-reacted starting material needs to be separated, while hydrogenated products need to be raised in optical purity by some means or other.